1. Field of the Invention
The present invention relates to the field of liquid crystal display, and in particular to a method for speeding up rotation of liquid crystal molecule and a liquid crystal panel drive circuit used in the method.
2. The Related Arts
A liquid crystal display is a displaying device that comprises two parallel glass substrates that are opposite to each other and liquid crystal molecules arranged between the two substrates, wherein electrical excitation is applied to use anisotropy to effect switching of light. By means of the anisotropy of refraction of liquid crystal molecule, application of electrical voltage to the liquid crystal molecule to redefine refraction anisotropic axis may control the luminance of transmitting light of liquid crystal molecule.
Liquid crystal material used in a vertical alignment (VA) liquid crystal display device is generally liquid crystal molecule having negative dielectric anisotropy. Without application of electricity, the liquid crystal molecules are aligned in a direction that is substantially perpendicular to glass substrates. When an electrical voltage is applied, the liquid crystal molecules start to rotate along a vertical axis and the maximum rotation may reach being parallel with the glass substrates.
When the liquid crystal molecules are perpendicular to the glass substrates, the transmittance thereof is generally zero and displaying is darkest in a normal black mode. When the liquid crystal molecules are parallel with the glass substrates, the transmittance thereof is the maximum and displaying is brightest in the normal black mode. However, in a practical application, such a liquid crystal displaying manner often suffers an phenomenon of extension of response time for conversion from black to halftone, which are typically conversion from black to low luminance halftone, conversion from black to high luminance halftone, and conversion from black to white and then conversion back to black.
The primary factor that causes the extension of response time of a liquid crystal display device for conversion from black to halftone is that the rotational speed and the rotational angle of the liquid crystal molecule are determined by the magnitude of drive voltage applied thereto. However, in the halftone conversion process, since the drive voltage that drives the rotation of the liquid crystal molecule is relatively small, the rotational speed of the liquid crystal molecule is slow and an extended response time may thus result.
In view of the above problems, a known solution is to increase the drive voltage in order to increase the rotational speed of the liquid crystal molecule and thus shorten the response time. However, increasing drive voltage may result in an abrupt rise of transmittance, followed by a rapid drop, when the liquid crystal display device is converted from a bright condition to a dark condition, and no smooth transition may apply. Referring to FIG. 1, a drive voltage applied to a pixel electrode comprises a plurality of high levels Vp1 that may not be all identical and a plurality of low levels Vp2 that may not be all identical. The absolute value of the difference between adjacent high level and low level is ΔV. Referring to FIG. 2, when the ratio Vp1/Vp2 gets large, ΔV is large, so that the instantaneous change of transmittance is relatively large, making it purge that causes flicking of the liquid crystal display screen.